Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Law and Edict
It was at this period, moreover, that law and edict were separated. The distinction indeed had its foundation in the essential character of the Roman state; for even the regal power in Rome was subordinate, not superior, to the law of the land. But the profound and practical veneration, which the Romans, like every other people of political capacity, cherished for the principle of authority, gave birth to the remarkable rule of Roman constitutional and private law, that every command of the magistrate not based upon a law was at least valid during his tenure of office, although it expired with that tenure.
It is evident that in this view, so long as the presidents were nominated for life, the distinction between law and edict must have practically been almost lost sight of, and the legislative activity of the public assembly could acquire no development. On the other hand it obtained a wide field of action after the presidents were changed annually; and the fact was now by no means void of practical importance, that, if the consul in deciding a process committed a legal informality, his successor could institute a fresh trial of the cause.
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Reference address : http://www.ellopos.net/elpenor/rome/2-01-constitution-magistrate.asp?pg=31